the fall off for most things people sign up for is considerable, commercial gyms over sell memberships by about 500 % as they know most of them are never going to turn up after the first week unless it for a skinny latteI remember hearing a stat somewhere, and I think it may have been on the Art of One Dojo YouTube channel, that 50% of students who start TMA don't stick around past 3 months (or something like that, numbers could be off some). This is consistent with my anecdotal observations. That's not going to do much for anyone.
Even if what I said above was a non-issue, that's not a good analogy. You continuously train for things that do not occur on a regular basis. Like fighting. If you're driving your car to work and back everyday, you're already staying sharp from that.
gym fees seem to exist almost entirely as a fat guilt tax
that said if you can learn to drive to the point your allowed to take a killing machine out in public in three, months
then you should be able to learn to fight to a reasonable standard in the same time frame, admittedly some tma make this a difficult proposition, as they move at glacial speed, your likely to spend three months learn to move your left foot and your arm in a circle, which may be why so many quit?